Explosion proof dead front electrical receptacle having microswitch means



. Feb. 2, 1965 J. F. HEALY 3,168,624

EXPLOSIONPROOF DEAD FRONT ELECTRICAL RECEPTACLE HAVING MICROSWITCH MEANSFiled Feb. 15, 1961 2 Sheets-Sheet 1 f m ENTOR BY I Feb. 2, 1965 J. F.HEALY 3,163,624

EXPLOSION PROOF DEAD FRONT ELECTRICAL RECEPTACLE HAVING MICROSWITCHMEANS 2 Sheets-Sheet 2' Filed Feb. 13, 1961 United States Patent OfificeEXPLOSION PRGOF I)EAD FRONT ELECTRICAL RECEPTACLE HAVING MICROSWITCHMEANS Joseph F. Healy, Westport, Conn., assignor to Harvey Hubbell,Incorporated, Bridgeport, Conn., a corporation of Connecticut Filed Feb.13, 1961, Ser. No. 88,872

4 Claims. (Cl. 20051.09)

This invention relates to an electric outlet receptacle, particularly toa so-called explosion proof dead front electrical receptacle for use inlocations where there might be danger of explosion from gases or vapors,such, for example, as operating rooms of hospitals. It has for an objectto provide a receptacle of this character of a construction which willreduce to a minimum danger of explosion in such locations, and also inwhich there is no danger of operators being injured by coming in contactwith the receptacle.

Another object is to provide a receptacle of this type in which theattachment plug-in cap may be locked in the receptacle after insertiontherein by limited relative turning movement of the cap, and in whichthe electrical supply circuit to the receptacle contacts and the cap isnormally open and is closed by this turning movement and opened byreverse movement of the cap in the opposite direction to unlock this capand permit its removal from the receptacle.

It is also an object to provide an electrical receptacle in which theadvantages and favorable characteristics of microswitches may beutilized to control the electrical supply current to the receptacle.

It is a further object to provide a simplified construction and onewhich will require a relatively small space for its installation.

With the foregoing and other objects in view, I have devised theconstruction illustrated in the accompanying drawings forming a part ofthis specification. It is, however, to be understood the invention isnot limited to the specific details of construction and arrangementshown, but may embody various changes and modifications within the scopeof the invention.

In these drawings:

FIG. 1 is a longitudinal vertical section showing the receptacle appliedto a wall structure;

FIG. 2 is a rear view of the receptacle with the backing member removed;

FIG. 3 is a section of the base portion of the insulating insertstructure taken substantially on line 33 of FIG. 4; a

FIG. 4 is a rear view thereof taken substantially on line 44 of FIG. 3;

FIG. 5 is a partial section and front view of the device of FIG. 3 takensubstantially on the plane of line 55 of FIG. 3;

FIG. 6 is an exploded view of the receptacle and Wall mounting with theoutlet box of the house wiring system;

FIG. 7 is a transverse section showing a portion of the receptaclecontaining the receptacle contacts and the attachment plug cap insertedin the receptacle;

FIG. 8 is a partial front view of the receptacle taken substantially online 8-8 of FIG. 1;

FIG. 9 is an inner end view of the attachment plug cap;

FIG. 10 is an end view and partial section of the microswitches andmeans for operating them taken substantially on the plane of line 1010of FIG. 11;

FIG. 11 is a partial detail view looking from the right of FIG. 10, and

FIG. 12 is an elevational view looking toward the bottom of FIG. 10,"asindicated by line 12-12.

A dangerous hazard in the use of outlet receptacles with attachment plugcaps which may be plugged into 3,168,624 Patented Feb. 2, 1965 andremoved from the receptacle in providing electrical connection forsupplying current to various electrically operated devices orattachments, particularly in such locations, for example, as operatingrooms of hospitals where there may be anaesthetic fumes, or otherlocations where explosive or combustable gases may be involved, isdanger of sparks or arcing produced in operation of insertion orremoving the plug-in cap causing a fire or an explosion, and it is theprincipal object of this invention to provide a construction in whichsuch danger is entirely removed, or at least reduced to a minimum.

A particular object is to provide a construction which will utilize theadvantages of a microswitch control for the receptacle in which themicroswitch means is in a sealed compartment so that any arcing in theoperation of the switch means will not ignite any combustible gases inthe surrounding atmosphere.

It is also an object to provide a structure in which the switch isalways in the off or circuit open position when the attachment plug capis inserted in the receptacle to establish electrical contact betweenthe contacts of the cap and receptacle, or withdrawn from the receptacleto separate the contacts of the plug and receptacle, so that there willbe no sparks formed by these operations, and as a further safety meansthe cap is always locked against withdrawal from the receptacle when theswitch means is closed to close the circuit to the receptacle contacts,and is unlocked so as to be withdrawable from the receptacle only whenthe switch means is in the open position and the circuit to thereceptacle contacts is broken.

This improved receptacle comprises a body member 1 including a flange 2of a size and adapted to cover an opening 3 in a wall structure 4leading to the wiring system for supplying electrical current. The wallmay be of any suitable structure, such as plaster 5 covered with asuitable tile 6, and provided with an opening 3 leading to a wall outletbox 7 of the electrical wiring system to which the conductor wires ofthe system may be led through suitable protective conduits 8 connectedat 8' to the box. The body member 1 may be of any suitable material,preferably a suitable metal, such, for example, as bronze, and includesa hollow or tubular forward extension 9 enclosing a chamber 10 open atboth its outer and inner ends. Mounted in this chamber is an insulatinginsert structure comprising a body portion 11 and a base portion 12.These may be molded in one piece, but preferably comprise two memberssecured together by lonigtudinal screws 13 in the body portion 11 andthreaded at their inner ends into inserts 14 molded in the base portion12, the inner end of the portion 11 being seated in a recess 15 in thefront wall of the base portion 12. This portion is secured to the bodymember 1 by suitable means, such, for example, as a screw threadedengagement 16.

The body portion 11 is a tubular portion enclosing a chamber 17 havingan entrance opening 18 at its outer end, and in which chamber aremounted the receptacle contacts 19 and 20, one of which, in this casethe contact 20, may be a grounding contact, while the others may beconnected with the wiring supply system through the switch means toreceive current from this system. These contacts 19 and 20 are in theform of substantially flat, longitudinally extending blades mounted onthe front side of the base portion 12 by suitable rivet-type inserts 21and 22 (FIGS. 3, 4 and 5), by means of laterally extending feet 23 and24, one on each contact, provided with an opening to receive the end ofthe rivet which is then riveted over to secure the contacts, theserivets extending through the base pontion 12, as shown in FIG. 3,forming electrical connection with the receptacle contacts 19 and 20.These feetare also preferably seated in recesses 25 in the front surfaceof the base memprovided with a curved, wider portion 26 and 27 for apurpose presently to be described. They are also preferably mounted inlongitudinally extending recesses 28 in the inner walls ot the chamber17 with a longitudinally extending, substantially fiat spring 29 at therear side of each one to assist in keeping the contacts in properposition.

. To connect the receptacle contacts 19 with the supply of a housewiring system, there is mounted on the inner or rear side of the baseportion 12 a-microswitch means, in the present case comprising twomicroswitches 3t? and 31 connected with the house system through thewall outlet box 7 by means of the supply conductors 3-2 and 33, oneswitch controlling one side of the circuit from the conductor 32 to oneof the receptacle contacts 1'9, and the other controlling the other sideof the circuit from the conductor 33 to the other receptacle contact 19.A single microswich of the proper capacity could be used, but it ispreferred to use two microswitches, one controlling each side of thecircuit, as shown. These switches are mounted on the rear side of thebase portion 12. For this purpose there are provided two brackets 34each comprising a flat metal strip provided with lateral feet 35' (FIGS.3 and 4) provided with openings to receive the inner ends of two of theinserts 1 and then rolled over to secure these feet to the insert and tothe member 12. These inserts are so located that the two brackets 34 arein alignment and in the same plane, as indicated in FIGS. 2, 4 and 10,and they are provided with wider end portions 36 provided with elongatedopenings 37. The two microswitches may be purchased complete andassembled on the market, and include insulating body portiors 38 whichmay be positioned on opposite sides of the free end portions 36 of thebrackets 34 and secured thereto by transverse screws 39 passing throughthese insulating bodies and through the openings 37 in the brackets. Thescrews may be provided with countersunk nuts 40 in recesses in the sidesof the bodies 33, and threaded onto screws 39 to securely clamp the twoswitches to the opposite sides of the brackets 34. The conductor wire 32is connected to one contact ot the switch 31 by the connecting member 41and screw 42 (FIGS. 2 and 4), while the other conductor 33 is connectedto similar contact 30 by the connector 43. The

other contact of the switch 31 is connected by a clip or conductor 44and conductor wire 45 by :one of the inserts 21 to one of the receptaclecontacts 19 through the clip 4-6, which is perforated to seat over theinner end of this insert, and which is rolled or riveted over the clipto secure it to the insert. The insert therefore provides electricconnection between the microswitch 31 and the receptacle contact.Similarly, the other microswitch 3,0is electrically connected to theother receptacle con tact 1) by the clip 47, conductor wire 48 and clip49 connected to the end of the other insert 21 connected with the otherreceptacle contact 19.

The micrcswitch means is enclosed in a sealed chamber 50 formed by thebody member 1, base member 12 and a backing member 51. This backingmember is a flanged member with a rearwardly extending hollow portion 52in which is provided a portion of chamber 59, and it is closed at itsrear side but is open at the front side facing body member 1. It issecured to the rear or inner side of the body member 1 by suitablescrews 53 extending through the flange portion of the member 51 andthreaded into the body member 1. Thus the microswitch means is enclosedin a sealed chamber 50 .provided by this backing member, the base member12 and the body member 1. The forward portion of this chamber may be inthe rear side of the member 1, as shown at 54. The portion of thischamber within the backing member 51 may be lined with a fiberinsulating lining 55. Its rear wall is provided with a tubular ex- Vtension 56 having an opening 57 for passage of the two conductor wires32 and 33, and this opening or passage may be sealed by a suitablesealing wax 58, so that the microswitch means and its operating meansare entirely enclosed in a sealed chamber. To insure a sealed connectionbetween the backing member 51 and the body member 1, a portion 64 of therear surface of the body member 1 is finished to an accurate flatsurface to form a seat forthe similarly finished front surface 65 of thebacking member 51.

The receptacle including the body portion 1, the backing member 51 andthe elements mounted therein may be connected to the outlet wall box 7of the current supply system by means of a mounting block 59 secured tothe body member 1 and the backing member 51 by-suitable screws onpassing through openings 61) in the flange portions of the body memberand backing member, and threaded into the block 59. This block is screwthreaded on its outer surface, as indicated at 61, by which it may bethreaded into similarly threaded opening 62 in the front wall of the box7, as indicated in FIGS. 1 and 6. The block 59 is provided with anoblong or substantially rectangular shaped opening 53 to receive therearwardly extending port-ion 52 of the backing member 51, which FIG. 7,inserted in the receptacle. The insulating insert structure 11 is openat its forward end 18 for insertion of an insulating extension 67 of theplug. This plug comprises an insulating body member 6% provided with arecess 69 which may receive the inner end portion 70 of the insulatingextension 67. This portion 67 includes an enlarged intermediate portion71 by which the extension 67 is secured to the insert 68 by suitablescrews 72. Mounted on this insulating extension 67 are attachment plugcontacts 73 and 74, which are enlarged end portions of longitudinallyextending conductor strips 75 and 76 mounted in longitudinal channels inthe wall of the insulating extension 67, and provided with binding postscrews 77 and 78 to which may be connected the conductor Wires 79 and 80of an insulating cable 81 leading to the attachment or other apparatusto be operated and supplied with current from the wiring system. Thecontacts 73 are positioned and mounted to engage the receptaclecontacts19 connected through the rnicroswitch means to the house wiring system,while the contact 74 is a grounding contact for connecting to thegrounding wire 80 of the cable leading to the attachment. This ispreferably made of different size or wider than the contacts 73, and theopening 18 in the insert member 11 is shaped as shown in FIG. 8 so thatthe plug can be inserted in the receptacle in one position only; thus,the opening 13 as shown in FIG. 8 is provided with two narrower andproperly located recesses 82 for insertion of the narrower contacts 73,and a wider recess 83 to receive the wider grounding contact 74. Also,arrow means 84 and 85 may be provided on the receptacle and the end ofthe plug associated with a rib 86 and recess 87 to further insure thatthe plug may be inserted in the receptacle in one position only, toinsure that the contacts 73 engage only the contacts 19 and thegrounding contact 74 engages only the grounding contact 20.

The contact 74 may be grounded on a metal shell 88 enclosing the members68 and 71 by means of a conductor strip 89 connected to the strip 87with a laterally extending free end 90 engaging the inside of the shell88 and secured to the member 71 by a suitable screw 91. The outer end'ofthe chamber 17 in the receptacle is normally closed by a slidinginsulating closure 92. This slideswithin the chamber 17 and has alateral extension forming a shoulder 93 (FIG. 7) which may engage anoverhanging portion 94 adjacent the outer end of the chamber 17 to limitoutward movement of the closure 92. This member is normally held in itsouter or closed position by a suitable coiled spring 95.

Means is provided to control operation of the microswitch means 30, 31by the inserted attachment plug 66. For this purpose there is mounted inand extending through the base member 12 in a suitable bearing sleeve96, an operating shaft 97, and to secure it in the sleeve and alsoprovide a sealed passage the shaft may be threaded in the sleeve, asindicated at 98. Mounted on the inner end of this shaft is a cam 99secured to the shaft by riveting over the end of the shaft after passingit through an opening in the cam, as indicated at 100. This cam is inthe form of a plate provided with oppositely extending lugs 101 providedwith inclined cam surfaces 102 on one edge adapted to slide overinclined spring members 103 secured at one end by suitable rivets 104 tothe insulating bodies of the microswitches 30 and 31, as shown in FIGS.10, 11 and 12. These springs are inclined upwardly and outwardly fromtheir anchored ends and extend in opposite directions on the twomicroswitches, as indicated in these figures. The free ends are providedwith V-shaped channels 105 on their under sides receiving the free endsof operating buttons or plungers 106 of the switches. The cam 99 isnormally held in the retracted position by a coil spring 107 one end 108of which is secured to the cam, while the other end 109 is held behindone of the switch supporting brackets 34. This spring is so tensioned asto normally hold the cam in its retracted position with the switches intheir open position, and also tends to return the cam to this positionwhen released. At its outer end the shaft 97 is provided with anoncircular end 110, in the present case a flattened end portion, todetachably interlock with a similarly shaped recess 111 in the end ofthe extension 67 of the attachment plug cap 66. This flattened end ofthe shaft and the channel or recess 111 of the plug are so located thatnormally they are at right angles to the line joining the rivets orinserts 14 mounting microswitch supporting brackets 34, so that theflattened end 110 will seat in the recess 111 as the plug is inserted inthe receptacle.

It will be noted that the contacts 73 and 74 of the attachment plug capproject outwardly from the surface of the insulating extension 67 of theplug, so that they pass through the respective recesses 82 and 83, andby the longitudinal movement of inserting them with the extension 67 ofthe plug cap into the receptacle they engage the respective receptaclecontacts 19 and 20. It will be noted that in this action the closureplug or slider 92 is forced inwardly to the position of FIG. 7 to permitinsertion of the plug. This longitudinal inserting motion of the plug,however, has no action on the microswitch means, but the receptacle,including the chamber 17, is so constructed that after the plug isinserted in the receptacle, as shown in FIG. 7, it may be turned by alimited turning movement to a locked position in the receptacle. This isa limited turning movement clockwise after insertion of the extension 67into the receptacle. To secure the locking eifect the end wall 112 ofthe member 11 is extended to one side of the notches 82 and 93, asindicated at 113 and 114, and as shown in FIG. 8, and the widened freeend portions 26 and 27 of the contacts 19 and 20 extend in behind theseoverhanging portions of the end wall, so that as the inserted plug isgiven a limited turning movement the contacts 73 and 74 of this plugmove behind the shoulders or overhanging walls 113 and 114 and lock theplug against removal from the receptacle. The contacts 73 and 74 of theplug engage the contacts 19 and 20 of the receptacle by the longitudinalmovement of inserting the plug in the receptacle to form electricalcontact between the plug contacts and the receptacle contacts, and thewidened portions 26 and 27 of the receptacle contacts maintain thiselectrical contact between the plug and receptacle contacts during theturning movements of the plug to and from the locking position. It willbe seen that this turning movement of the inserted plug also turns theshaft 97 by the interlocked action between the end of the shaft and theelongated recess 111 in the plug. This turning of the shaft operates thecam 99, and its cam surfaces 102 by sliding over and depressing theinclined springs 103 depress the operating plungers 106 of themicroswitches to shift the switches to their on or closed position, itbeing a structure of these switches that they are normally in the off oropen position and when the pressure on the plungers 106 is releasedautomatically return to the open position. This operation of the cam onthe switches closes the supply circuit to the receptacle contacts 19 tosupply current to the inserted plug and the cable 81 leading to theattachment or other device to be supplied with curernt from the wiringsystem. To assist in retaining the cap in the locked position in thereceptacle the outer surface of the sliding closure 92 may be providedwith radial ribs 92' adapted to seat in similarly arranged grooves orchannels 67 in the end of the extension 67 of the plug cap.

The other contact 20 of the receptacle may be grounded on the bodymember 1 by a grounding strip mounted on the base portion 12 by aninsert rivet 22 fastening the contact 20 to the member 12, and the strip115 connected to the body member 1 by a suitable screw 116, as shown inFIG. 2.

It will be seen that the inserted plug may be returned to the unlockedposition so that it may be withdrawn from the receptacle by a relativeturning movement counterclockwise or backward to its first positionafter it is inserted in the receptacle. This movement removes the plugcontacts 73 and 74 from their locked position under the overhangingwalls 113 and 114 and permits withdrawal of the plug from thereceptacle. This movement, together with the action of the spring 107,returns the cam 99 to its original or off position, this movement beinglimited and the position determined by stop shoulders 117 on the lugs101 of the cam engaging the mounting brackets 34 for the switches, asshown in FIG. 4. This movement of the cam permits the microswitches tomove automatically to their open circuit position, cutting off thesupply of current from the house wiring system to the receptaclecontacts 19. The attachment plug cap 66 now being in the unlockedposition may be withdrawn from the receptacle.

It will be seen from the above that the making of the contact orengagement between the cap contacts and the receptacle contacts iseffected by the longitudinal movement of the plug as it is inserted inthe receptacle, and that this electrical contact between the capcontacts and the receptacle contacts is maintained during turningmovements of the cap to and from the locked position. It is also seenthat the electrical contact of the cap contacts to the receptaclecontacts is made and broken only when the microswitches are in theiropen position, so that this contact and separation of the cap andreceptacle contacts is effected only when the receptacle contacts aredead or are not connected to the house wiring system. There is,therefore, no chance of sparking in the operation of making or breakingcontact between the cap contacts and the receptacle contacts. Also, thecircuit and current supply to the receptacle contacts is on or closedonly when the inserted attachment plug cap is in the locked position,and the cap therefore cannot be removed or withdrawn from the receptaclewhen the receptacle contacts are alive or connected to the currentsupply system.

1. In combination, a wall having an opening; a closed outlet box of anelectrical supply wiring system mounted in said wall provided with afront wall having a threaded opening in alignment with the wall opening;a receptacle 7 including a body member-secured to the wall to cover thefirst openingand provided with a chamber; an insulating structuremounted in' said chamber; stationary receptacle contacts mounted in saidinsulating structure adapted for engagement With the contacts of anattachment plug cap inserted in said insulating structure; microswitchmeans mounted at the rear side of said insulating structure andelectrically connected with the receptacle contacts to control currentsupply thereto; operating mean for said microswitch means operable byturning movements of a plug cap inserted into the receptacle; a backingmember provided with a chamber enclosing the microswitch means; meanssecuring said backing member to said body member with the backing memberand body member providing a sealed chamber enclosing the microswitchmeans and its operating means; a mounting block in the form of anadjusting ring rigidly secured to the back of said body member andbacking member and having a threaded portion arranged to be thread-edlysecured in said threaded opening in the outlet box.

2. An electrical receptacle comprising: a body member including a hollowforward portion open at its opposite ends and a flange portion at theinner end thereof ar' ranged to cover a wall opening leading to a housewiring system; an insert structure of insulating material mounted insaid hollow portion; stationary receptacle contacts mounted in saidinsert'structure; said insert structure being open at its outer end forinsertion of an attachment plug cap having contacts to engage thereceptacle contacts; means in the insert structure adapted to cooperatewith the cap to lock the cap in the receptacle on relative turningmovement of the insert cap; microswitch means electrically connectedwith the receptacle contacts; means mounting said microswitch means onthe insert structure; said microswitch means including a housing and anoperating button; an associated-spring member secured to saidmicroswitch means housing and arranged to normally incline relativethereto in position to be moved toward and actuate said operatingbutton; operating means to control said microswitch means comprising ashaft and a cam on the inner end of the shaft arranged to actuate saidspring member to, in turn, cause it to actuate said operating button inresponse to turning movement of the from a house wiring system to themicroswitch means; a

backing member provided with a chamber enclosing the microswitch means;and means securing the backing mem-' ber to the rear of the body member,whereby the insert structure and backing member form a sealed chamberenclosing the microswitch means andthe operating means for controllingit.

e 3. An electrical receptacle as defined in claim 2 wherein saidmicroswitch means comprises apair of micr-oswitches which are secured tothe rear of said insert structure by bracket means disposed between saidpair of microswitches. a

4. An electrical receptacle of claim 2 wherein said insert structure isprovided with holding means anranged to cooperate with holding means onthe contacts of an associated attachment plug cap to lock the cap in thereceptacle by turning movement of the inserted cap; said receptaclecontacts are located to be engaged by the cap contacts as they areinserted into the receptacle are of a width to maintain contact as thecap is turned to and from the locking position; and wherein saidmicroswitch operating means is operative to move said spring member tooperate. the said operating button to close acircuit to the receptaclecontacts only when the cap is in the locked position.

References Cited in the file of this patent UNITED STATES PATENTS2,181,829 Jeffrey Nov. 2 8, 1939 2,441,465 I Bauroth May 11, 19482,646,475 Goodrich et a1 July 21, 1953 2,752,465 MacDonald June 26, 19562,857,486 Hubbell et al Oct. 21, 1958

1. IN COMBINATION, A WALL HAVING AN OPENING; A CLOSED OUTLET BOX OF ANELECTRICAL SUPPLY WIRING SYSTEM MOUNTED IN SAID WALL PROVIDED WITH AFRONT WALL HAVING A THREADED OPENING IN ALIGNMENT WITH THE WALL OPENING;A RECEPTACLE INCLUDING A BODY MEMBER SECURED TO THE WALL TO COVER THEFIRST OPENING AND PROVIDED WITH A CHAMBER; AN INSULATING STRUCTUREMOUNTED IN SAID CHAMBER; STATIONARY RECEPTACLE CONTACTS MOUNTED IN SAIDINSULATING STRUCTURE ADAPTED FOR ENGAGEMENT WITH THE CONTACTS OF ANATTACHMENT PLUG CAP INSERTED IN SAID INSULATING STRUCTURE; MIRCOSWITCHMEANS MOUNTED AT THE REAR SIDE OF SAID INSULATING STRUCTURE ANDELECTRICALLY CONNECTED WITH THE RECEPTACLE CONTACTS TO CONTROL CURRENTSUPPLY THERETO; OPERATING MEANS FOR SAID MICROSWITCH MEANS OPERABLE BYTURNING MOVEMENTS OF A PLUG CAP INSERTED INTO THE RECEPTACLE; A BACKINGMEMBER PROVIDED WITH A CHAMBER ENCLOSING THE MICROSWITCH MEANS; MEANSSECURING SAID BACKING MEMBER TO SAID BODY MEMBER WITH THE BACKING MEMBERAND BODY MEMBER PROVIDING A SEALED CHAMBER ENCLOSING THE MICROSWITCHMEANS AND ITS OPERATING MEANS; A MOUNTING BLOCK IN THE FORM OF ANADJUSTING RING RIGIDLY SECURED TO THE BACK OF SAID BODY MEMBER ANDBACKING MEMBER AND HAVING A THREADED PORTION ARRANGED TO BE THREADEDLYSECURED IN SAID THREADED OPENING IN THE OUTLET BOX.